Wound dressings, or simply dressings, are quantitatively characterized by a number of different parameters such as their: geometry (e.g., size, shape, number of layers and thickness of each layer), material composition (e.g., of each layer, including the use of polymer coatings, etc), conformality (e.g., their ability to conform to the topography of the skin surface), mechanical properties (e.g., tensile strength, elasticity), surface properties (e.g., flat, dimpled, textured, etc), moisture management (e.g., wicking, wetting, moisture penetration, hydrophilic, hydrophobic, evaporation, etc), mode of sterilization, anti-microbial, anti-fungal and/or anti-biotic properties, air permeation, vapor permeation, vacuum compatibility, hypoallergenic properties, textile properties (e.g., thread count, warp, weft, weave, cutting properties (edge fraying), etc), infused medicinal content (if any), color, ergonomics, mean time to replacement and the various adhesion mechanisms used for holding them in place, among other things.
A long-standing goal of the medical community in general is to select these various dressing parameters to minimize the “mean time to wound healing” (MTWH) for a highly diverse population of patients, with a highly diverse set of wound conditions, all-the-while adhering stringently to any and all Rules & Regulations imposed by the Food and Drug Administration (FDA), and to implement high-volume manufacturing methods that would enable inexpensive world-wide accessibility.
Traditionally, dressings were made of gauze pads or bandages made from natural and/or synthetic materials wherein wound exudate would be absorbed by the dressing to keep the wound dry and to help prevent the ingress of harmful bacteria. More recently, however, it has been shown that wounds heal faster and more efficiently when they are kept moist.
It has been known for many years that certain metals possess anti-microbial, anti-bacterial, anti-fungal, anti-biotic and/or other medicinal properties when introduced into a wound system (see for example, Von Nageli, “On the Oligodynamic Phenomenon in Living Cells”, Denkschriften der Schweizerischen Naturforschenden Gesellschaft, Vol. 33, No. 1, p. 174, 1893 and McKhann, Carlson, and Douglas, “Oligodynamic Action of Metallic Elements and of Metal Alloys on Certain Bacterial and Viruses”, Pediatrics, Vol. 2, p. 272, 1948). These metals include: silver (Ag), gold (Au), platinum (Pt), palladium (Pd), copper (Cu), and zinc (Zn), among others. Of these, however, silver is perhaps the best known.
Anodic silver at low direct currents is known to have inhibitory, anti-bacterial and/or anti-fungal properties. See for example, Berger, (“Antifungal Properties of Electrically Generated Metallic Ions”, Antimicrobial Agents and Chemotherapy, Vol. 10, No. 5, November 1976, p. 856) and Spadaro (“Antibacterial Effects of Silver Electrodes with Weak Direct Current”, Antimicrobial Agents and Chemotherapy, Vol. 6, No. 5, November 1974, p. 637).
Additionally descriptive of antimicrobial surfaces comprising two or more metals in contact with a body electrolyte that produces galvanic action is U.S. Pat. No. 4,886,505 to Haynes et al. Other patents which describe galvanic cells and galvanic elements, include U.S. Pat. No. 5,685,837, Horstmann; and U.S. Pat. No. 6,365,220 to Burrell, which are incorporated by reference herein. However, prior art approaches are lacking in numerous respects. For example, Burrell's approach requires multiple evaporations of different metals and subsequent metal etching techniques that, more-often-than-not, require the use of highly corrosive chemicals and/or toxic gas plasmas (such as chlorine and/or fluorine). More importantly, nowhere in Burrell's work does he mention the use of metallic anti-microbial nanospheres suspended in an array of biodegradable polymer nano and/or micropillars.
U.S. Pat. No. 7,457,667 to Skiba, which is also incorporated by reference, describes a current-producing wound dressing but does not suggest using micropillars to increase the contact surface area between the wound electrolyte and the galvanic surface. Skiba also fails to mention the important class of biodegradable polymers that can be used for a controlled release of the metallic ions. Instead, he refers only to “biocompatible binders” that are used in making the inks. Skiba describes a more traditional surface effect to wound healing. This can be considered a two-dimensional approach to wound healing because the ink described in this reference is in proximal contact with the wound surface, and is not inserted into a wound, which can be considered a three-dimensional approach to wound healing. For example, in a three dimensional approach to wound healing, protuberances or pillars are actually inserted into the wound for a three dimensional response.